Future imaging and communication systems will extend the need for higher frequency and bandwidth devices and circuits beyond current device capabilities. The current generation of millimeter wave (mmW) transceivers and imagers are operable at frequency bands between 50-120 GHz. Further, mmW components, such as amplifiers, operable in G-band frequencies (140-220 GHz) have also been developed.
Lithography techniques such as electron beam lithography (EBL) and X-ray lithography are conventionally used in semiconductor device fabrication processes to manufacture mmW semiconductor devices. In an EBL semiconductor fabrication process, a semiconductor wafer is first coated with a photoresist and a window pattern is developed and made in the photoresist by an electron beam (e-beam). A metal is deposited in the window pattern and over the photoresist. The photoresist is then stripped or lifted off from the wafer so that only the gate metal remains. The EBL semiconductor fabrication process can achieve a gate having a gate capacitance sufficiently low for high frequency applications, such as the mmW transceivers discussed briefly above.
The next generation of technologies will operate in the sub-millimeter wave to provide benefits such as higher available bandwidth, reduced radar aperture and instrument size, and narrowed beam widths for radar and remote sensing applications by utilizing frequencies from 300 GHz to 3 THz.
However, conventional semiconductor device fabrication processes, such as the EBL semiconductor device fabrication process discussed above, cannot alone manufacture semiconductor devices such as transistors suitable for sub-millimeter wave operation. Particularly, the EBL semiconductor fabrication process cannot achieve a transistor gate having a gate capacitance sufficiently low enough for operating in frequencies from 300 GHz to 3 THz.
Further, in addition to imaging and communication systems, there is a continuing trend in the semiconductor industry toward higher device densities. To achieve these high densities there have been, and continue to be, efforts toward scaling down device dimensions at submicron levels on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller feature sizes are required.
It would be desirable to have an EBL semiconductor device fabrication process that would enable the manufacture of semiconductor devices suitable for sub-millimeter wave operation. It would be further desirable for such an EBL semiconductor fabrication process to also satisfy the production efficiency and complexity levels of current semiconductor device fabrication processes for manufacturing mmW components. It would be further desirable for such an EBL semiconductor device process to have repeatability and robustness in a manufacturing environment.